Technical Field
Aspects of the present disclosure generally relate to an image forming apparatus, such as an electrophotographic copier, a printer, a facsimile machine, and a multifunction peripheral (MFP).
Related Art
In an electrophotographic image forming apparatus, a cleaning blade removes residual toner from an intermediate transfer belt to clean the intermediate transfer belt. With an increase in degree of circularity of toner, high-resolution and high-quality images are achieved. However, removing toner of high circularity with the cleaning blade is difficult.
In an electrophotographic image forming apparatus that is capable of outputting color images, toner employed for plural colors, such as yellow, magenta, cyan, and black, differs in degree of circularity between the colors.
In this case, the degree of circularity is equal to a ratio of a perimeter of a circle having the same area as a projected area of toner particles relative to a perimeter of a projected image of toner particles.
When the electrophotographic image forming apparatus repeatedly forms images, toner within a developing device is less likely to be replaced with new toner with a lower printing ratio that is a ratio of an area to be printed relative to an area of a transfer sheet which allows an image to be formed because a less amount of toner is moved from a developing roller to a photoconductor, to be developed into a toner image. As a result, the toner remains within the developing device for a longer time. The toner remaining within the developing device for a long time is stirred and applied with stress for a long time, thereby degrading the charging capability and charge retaining capability, resulting in a deterioration in quality of images due to cleaning failure. When toner is maintained charged for a long time, the toner accumulates within the developing device due to stress by the friction and pressure of the developing blade and the developing roller. Such toner remaining within the developing device for a long time is referred to as “degraded toner”.
To prevent a deterioration in quality of images due to degraded toner adhering to the developing roller within the developing device, a “refresh” process is performed to replace toner stored within the developing device with new fresh toner, that is, refresh toner. Specifically, an average printing area ratio and the distance of rotation of a toner supply roller are employed such that old toner is discharged from the interior of the developing device to the photoconductor at a predetermined timing and a toner pattern is formed between transfer sheets on the intermediate transfer belt. Then, new toner is resupplied to the developing device, thus preventing degraded toner from remaining within the developing device for a long time. Such a manner to “refresh” toner within the developing device improves the image quality.
To improve the cleanability of a photoconductor cleaner, a forced discharge process for discharging toner from a developing roller, i.e., the refresh process, is performed in which toner of irregular shapes to be successfully removed by the photoconductor cleaner is forced to enter the photoconductor cleaner and toner of a spherical shape to be unsuccessfully removed by the photoconductor cleaner is forced to reach a belt cleaner. Alternatively, a mass of toner with a constant ratio between an irregular shaped toner and a spherical toner is input to each of the belt cleaner and the photoconductor cleaner, thereby improving the cleanability of the cleaners. However, even with changes in a mixture ratio of the irregular shaped toner and the spherical toner, when the spherical toner first reaches the belt cleaner or the photoconductor cleaner, a cleaning failure may occur.